1 Field of the Invention:
The present invention relates to a zinc oxide type lightning-conducting element with electrodes having excellent properties.
2 Related Art Statement:
As conventional lightning-conducting elements mainly composed of zinc oxide for protecting insulators from high voltage surge due to lighting, has been is known, as sectionally shown in FIG. 3, that electrodes 12, made of such materials as aluminum, are formed on opposite surfaces of a ZnO element 11 by a metal flame spraying process. The ZnO elements 11 is a metal oxide sintered body which mainly consists of zinc oxide and at least one kind of metal oxide additive.
In the above-constituted zinc oxide type lightning-conducting elements, the metal flame-sprayed electrodes 12 reduce a contact resistance in piled lightning-conducting elements and uniformly distribute current flowing inside the lightning-conducting elements.
The metal flame-sprayed electrodes 12 used as electrodes in the above-mentioned conventional zinc oxide type lightning-conducting have large sprayed particles and as a result, portions at which the electrode does not contact the ZnO element 11 are formed to a cerain degree at uneven surface portions thereof. Consequently, when the lightning-conducting element operates due to a great current surge such as a lightning impulse current, discharge locally occurs and current does not uniformly flow through the ZnO element 11. Consequently, the essential characteristics of the ZnO element cannot fully be exhibited and the lightning-conducting element may be broken even under a low surge current.
Japanese patent application Laid-open No. 61-171,102 discloses a technique for uniformly forming metal electrodes of fine particles on surfaces of a ZnO element by vapor deposition. However, the electrode on the surface of the ZnO element is broken due to surge currents unless the electrode has a thickness of larger than 5 to 10 .mu.m, so that a stable effect cannot be attained. On the other hand, it is economically difficult to obtain a thickness of not less than 5 to 10 .mu.m by vapor deposition only. Therefore, satisfactory performances as the lightning-conducting elements could not be obtained.